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  1. #1
    Join Date
    Sep 2007
    Posts
    1

    Smile PT Decking wet, dry, or inbetween.

    I need some advice. I am building a new deck.(in process) I spent the part of the weekend setting up the layout for my decking. (PT pine PT decking 16FT)I have heard that the boards should be butted together and allowed to shrink, allowing proper gaps between the boards.I'm ok with that but decided to space them with a 4d finish nail. I got 3 boards down and left the project for a 1 day. Came back to the job and the decking has shrunk already. All the other boards have been laid out for a day ready to be installed. Question is do I continue to space them out or just but them all together and hope the gaps will be sufficient with more time to shrink down.
    I do appreciate all input.

  2. #2
    Join Date
    Aug 2007
    Posts
    1,131

    Default Re: PT Decking wet, dry, or inbetween.

    Rather than repeat recently posted info, please see http://advice.thisoldhouse.com/showthread.php?t=1038

    Your PT wood may or may not have been at full-blown fiber-saturation (FS) when you bought it and hauled it home. The wood you haven't laid yet may or may not be at the FS point yet. How much moisture it has or hasn't lost will be a direct result of how you have it stored......among other factors. (The fiber-saturation point is approx. 28% contained moisture and wood can't get any wetter than that once it's been kiln-dried. The FS point is likely a bit different for PT wood because the chemicals are taking up space inside the wood fibers. Whatever the actual number for PT lumber......the wood will be at FS when it's initially taken from the treatment chamber)

    Whether you should lay your boards tightly and just allow them to shrink down.....or whether you should sticker the stock and let it air-dry down for a couple weeks before you lay it (spaced).......is going to depend upon a couple factors.

    If you live in a climate with alot of rain (particularly prolonged days/weeks of sustained rainfall), then the lumber will likely reach FS again at some time.....IF you don't keep a viable coat of water repellent on it at all times. This means it would/could return to the same dimension as when it first came out of the treatment chamber. If it returns to the same dimension you have now and you lay them tight......the deck will hold water if/when it returns to the FS point. Think large puddles of water. (I know a couple guys who did this and now regret it. They aren't very diligent about keeping water repellant on their decks.) If you want to ensure that this can never happen, no matter what...... you actually need to ascertain that the lumber is at FS when you lay them and then space the boards just a tad to boot. However, this can mean that you end up with some fairly large gaps during the dry parts of the year. This might not appeal to you if the deck will spend most of the year with really big gaps.

    If it doesn't, then I'd suggest you sticker your lumber........out of the sun and rain.....and let it dry down for a couple weeks or more before you lay it. Good air flow around the stack is your friend. Run a big fan if necessary/desirable.....depending upon where you stack it. Then space the boards with a 16d common nail (not a sinker cause those have a much thinner shank). Then commit to keeping a viable coat of water repellant on it so it doesn't ever reach FS (expand enough to totally close up those gaps.....and potentially cause the floor to actually heave). You'll need to renew the water repellent at least every other year....if not every year. Yes, the lumber will still grow in dimension just from sustained high relative humidity levels, but that alone shouldn't be enough to close the gap on a 6" wide board. The boards will also shrink when conditions are drier. No water repellent or deck finish can totally prevent changes in the wood's dimension.
    Last edited by goldhiller; 09-06-2007 at 09:55 PM.

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